Noble metals and rare metals are widely used for industrial purposes for their excellent stability, catalyst activity, etc. However, because noble metals and rare metals are rare and expensive resources, effective utilization thereof is necessary. Therefore, it is important to efficiently collect and reuse noble or rare metal contained in used noble or rare metal-containing waste materials, such as waste catalysts for purifying automobile exhaust gas, waste catalysts for chemical industries, wastes generated in electronic circuit board manufacturing processes, waste electronic components, wastes of electrolysis electrode, and the like.
Typical examples of methods for collecting noble or rare metal include a wet method, such as a dissolution method comprising dissolving a metal component in a strong acid to thereby collect metal; and a dry method comprising collecting metal by absorption of a metal component into molten metal (see Non-Patent Literature (NPL) 1). However, various waste materials, such as electronic components, battery cells, catalysts, cellular phones, and automobile parts, contain noble or rare metal etc. Therefore, whichever method, i.e., wet or dry method, is employed for the collection, formation of processes or systems suitable for the properties of each of the materials is needed.
In a wet method, acids destroy the material itself of a waste material. Therefore, even if noble metal etc. is collected, the base material thereof cannot be reused. In addition, after-treatment of the dissolved residue is troublesome. Further, in a wet method, the dissolution rate of noble or rare metal by acid is low, and a waste material containing a smaller amount of noble or rare metal requires a relatively larger amount of acid. Furthermore, because strong acids must be handled with care and may cause adverse environmental effects, an increase in equipment investment is unavoidable.
With respect to the dry method, which uses a molten metal, such as iron, copper, lead, or the like, as a material for absorbing noble or rare metal, the efficiency of noble or rare metal absorption is not so high, the devices are costly because the method is performed at a high temperature, and thus expensive equipment is required. Further, at present, using molten lead is substantially difficult because it is environmentally harmful.